A vacuum-encapsulated silicon switch with a curved electrode is characterized for operation in harsh environments. An ultraclean vacuum encapsulation process (episeal) seals the switch after release, providing a pristine operating environment for switching operations. In these devices, the curved beam of the actuator enhances the overdrive voltage tolerance to be more than 100 V. The ON/OFF cycle tests were carried out up to $10^{5}$ cycles at room temperature, and at least $10^{4}$ cycles under an elevated temperature of 300 $^{circ}{rm C}$ . Throughout the 300 $^{circ}{rm C}$ tests, an average contact resistance of ${sim}{rm 28}~{rm k}Omega$ is measured, demonstrating the stability of the contact. Finally, high speed pulse $I{-}V$ monitoring unit was used to observe 13- $mu{rm s}$ switching speed.